Copolymers, polymer resin composition for buffer layer method of forming a pattern using the same and method of manufacturing a capacitor using the same

ABSTRACT

The invention is directed to particular polymer compositions that may be generally characterized by the formula: 
                         
wherein the variables L, M and N represent the relative molar fractions of the monomers and satisfy the expressions 0&lt;L≦0.8; 0&lt;M≦0.2; 0&lt;L≦0.35; and L+M+N=1; and, wherein R 1 , R 2  and R 3  are independently selected from C 1 -C 6  alkyls and derivatives thereof. The invention is also directed to polymer compositions that, when used to form a buffer layer or pattern, can be more easily removed from the surface of a semiconductor substrate, thereby increasing productivity and/or reducing the likelihood of defects and failures associated with residual photoresist material.

PRIORITY STATEMENT

This is a Divisional Application of, and claims priority under 35 U.S.C.§120 to, U.S. application Ser. No. 11/447,120, filed on Jun. 6, 2006 nowU.S. Pat. No. 7,514,319, which also claims the benefit of Korean PatentApplication No. 2005-0076529, filed on Aug. 20, 2005, in the KoreanIntellectual Property Office, the disclosure of which is incorporatedherein, in its entirety, by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention include polymeric compounds, andcompositions including such compounds, that may be used in formingbarrier layers for protecting underlying materials and structures andmethods of utilizing such compounds and compositions. For example,compounds and compositions according to example embodiments of theinvention may be used in manufacturing semiconductor integratedcircuits, particularly with respect to methods for forming photoresistbarrier layers and/or patterns that will provide satisfactory protectionfor underlying materials and structures while also simplifying thesubsequent removal processes.

2. Description of the Related Art

In fabrication processes used for manufacturing semiconductor devices,photolithographic processes are used repeatedly to form a wide varietyof films and patterns at different stages of the fabrication process. Assemiconductor devices have become more highly integrated, the criticalprocess dimensions, for example, the spacing between adjacent conductivelines, are being reduced accordingly. The increased degree ofintegration has led to other changes in the fabrication process as wellincluding, for example, delaying formation of capacitor structures untilafter formation of the bit lines in semiconductor memory devices such asDRAMs to provide additional surface area for capacitor formation. Theprocesses developed for forming capacitor structures typically include aseries of sacrificial and barrier layers that are used in combinationwith one or more of deposition, planarization and etch processes toobtain the desired structure(s).

Due to the technical requirements associated with achieving higherdegrees of integration in semiconductor devices, there has beencontinuing emphasis on reducing the surface area required for forming amemory cell in semiconductor memory devices. These efforts have led todifficulties in forming capacitors having a sufficient storagecapacitance within the memory cell. Various methods have been proposedand/or adopted for maintaining the capacitance of such storagecapacitors at acceptable levels in a reduced cell area. One approachinvolves increasing the height of the storage node by, for example,increasing the height of the lower electrode of a capacitor to form whatis widely referred to as a cylindrical capacitor.

Examples of such cylindrical capacitor structures are disclosed in U.S.Pat. Nos. 6,700,153 and 6,171,902, the disclosures of which are herebyincorporated, in their entirety, by reference to the extent consistentwith the present disclosure.

One such conventional method for fabricating a type of One CylinderStorage (OCS) capacitor that can be used, for example, as the chargestorage device in a DRAM memory cell, is illustrated in FIGS. 1A-1E. Asillustrated in FIG. 1A, a substrate is prepared with both insulatingregions 1, for example, an interlayer oxide, and a conductive regions 2,such as a contact plug or a pad plug for establishing electrical contactwith conductive regions formed below the conductive regions.

A stop layer 3 may then be formed on both the insulating regions andconductive regions 2, with a molding layer 4, typically formed from aninsulating material, for example, a silicon oxide, then being formed onthe etch stop layer 3. The molding layer is then patterned and etchedusing a suitable photolithographic process (not shown) to remove themolding layer 4 and the stop layer 3 from regions of the substrate toform an opening 6 and thereby expose an upper surface of the conductiveregion 2. This opening 6 formed in the molding layer will, in turn,serve as the “mold” pattern for the subsequently formed capacitorstructure. The photoresist pattern used as an etch mask (not shown) isthen removed and the exposed surfaces cleaned in preparation foradditional processing.

One or more layers of conductive material 7, 8, for example, a primaryconductive layer may be combined with a barrier layer and/or an adhesionpromoting layer in order to form a multilayer conductive stack structurehaving a desired combination of properties. One such combination ofmaterials used for forming conductive material layers 7, 8 is a metaland the corresponding metal nitride. The conductive material layer(s)are formed on the exposed surfaces of the mold pattern structureincluding the upper surface of the remaining portions of the moldinglayer 4, the sidewalls of the opening 6 and the surface of theconductive region 2 exposed at the bottom of the opening. As illustratedin FIG. 1B, an insulating buffer layer 10, for example, a CVD oxide, isthen formed on the conductive material 7, 8 to a thickness sufficient tofill the opening 6. As the aspect ratio of the opening 6 increases,however, the chance that the deposition will seal the mouth of theopening before completely filling the opening increases. In suchinstances, a generally centrally located void 12 will remain within theopening 6.

As illustrated in FIG. 1C, the upper portion of the insulating bufferlayer 10 can be removed using any suitable blanket etch or chemicalmechanical polishing (CMP) method to expose an upper surface of theconductive material 7, 8. As illustrated in FIG. 1D, the upper portionof the conductive material layers 7, 8 and additional upper portions ofthe insulating buffer layer 10 can then be removed using any suitablemethod (or combination of methods) including, for example, blanket dry(plasma) etch-back or CMP processing, thereby leaving only thoseportions of the insulating buffer layer 10 and the conductive materiallayers 7, 8 that were in the remaining portion of the opening 6.

As illustrated in FIG. 1E, the remaining portions of the molding layer 4and the insulating buffer layer 10 are then removed eithersimultaneously with an appropriate etch, for example a wet etch using alow ammonium fluoride liquid (LAL) etch composition or sequentiallyusing a sequence of suitable etch compositions and/or methods. Duringremoval of these layers, the remaining portion of the void 12 maycomplicate the processing by effectively reducing the thickness of theinsulating buffer layer 10 relative to the remaining portions of themolding layer 4.

Depending on the combination of conductive layer 7, 8 composition,insulating buffer layer 10 composition and the etch chemistry orchemistries utilized to remove these layers, the central portion of theconductive layers 7, 8 above the conductive region 2 may be exposed tothe etch composition for an extended period of time, thereby increasingthe possibility that one or more of the layers will be damaged,contaminated or breached. In such instances, the initial yield and/orthe reliability of the resulting devices may be degraded. After theremaining portions of the molding layer 4 and the insulating bufferlayer 10 have been removed, the remaining structures, in particular thelower electrode of the capacitor, make be cleaned to remove residualetch composition and water, for example, a sequence of deionized water(DI) rinses to a target resistivity followed by processing in anisopropyl alcohol (IPA) dryer.

Another conventional method for fabricating OCS capacitors that can beused, for example, as the charge storage device in a DRAM memory cell,is illustrated in FIGS. 2A-2G. As in FIG. 1 and as again illustrated inFIG. 2A, a substrate is prepared with both insulating regions 1, forexample, an interlayer oxide, and a conductive regions 2, such as acontact plug for establishing contact with conductive regions formedbelow the conductive regions.

A stop layer 3 may then be formed on both the insulating regions andconductive regions 2, with a molding layer 4, typically formed from aninsulating material, for example, a silicon oxide, then being formed onthe etch stop layer 3. The molding layer is then patterned and etchedusing a suitable photolithographic process (not shown) to remove themolding layer 4 and the stop layer 3 from regions of the substrate toform an opening 6 and thereby expose an upper surface of the conductiveregion 2. This opening 6 formed in the molding layer will, in turn,serve as the “mold” pattern for the subsequently formed capacitorstructure. The photoresist pattern used as an etch mask (not shown) isthen removed and the exposed surfaces cleaned in preparation foradditional processing.

One or more layers of conductive material 7, 8, for example, a primaryconductive layer may be combined with a barrier layer and/or an adhesionpromoting layer in order to form a multilayer conductive stack structurehaving a desired combination of properties. One such combination ofmaterials used for forming conductive material layers 7, 8 is a metaland the corresponding metal nitride. The conductive material layer(s)are formed on the exposed surfaces of the mold pattern structureincluding the upper surface of the remaining portions of the moldinglayer 4, the sidewalls of the opening 6 and the surface of theconductive region 2 exposed at the bottom of the opening. As illustratedin FIG. 2B, a photoresist buffer layer 14, for example, a novolak (alsowidely referred to as “novolac” in the art) resin-based photoresist, isthen formed on the conductive material 7, 8 to a thickness sufficient tofill the opening 6. Through selection of an appropriate photoresistcomposition in combination with an appropriate application technique,the photoresist buffer layer 14 may be formed without incurring thevoids associated with depositions of inorganic materials and illustratedin FIGS. 1B-1D, for example, CVD silicon oxide depositions, even inhigher aspect ratio openings 6.

As illustrated in FIG. 2C, an upper portion 14 a of the photoresistbuffer layer 14 can then be removed by exposing the upper portion of thephotoresist buffer layer to radiation having a combination of frequencyand intensity that will tend to breakdown or depolymerize the upperportion 14 a of the photoresist buffer layer 14 relative to the lowerportion 14 b of the buffer layer. This exposed portion of thephotoresist buffer layer can then be removed by using a suitabledeveloping solution, typically an alkaline solution for positivephotoresist compositions. As illustrated in FIG. 2D, after removing theupper portion 14 a of the photoresist buffer layer 14, a lower portion14 b of the photoresist buffer layer will remain in the opening 6 whileupper portions of the conductive layers 7, 8 are exposed. The lowerportion 14 b of the photoresist buffer layer can then be baked or curedat a temperature and for a bake duration sufficient to harden the lowerportion 14 b in order to increase its resistance to the etch solutionsused to remove the remaining portions of the molding layer 4.

As illustrated in FIG. 2E, any suitable blanket etch or CMP method maythen be utilized to remove an upper portion(s) of the conductivematerial 7, 8 using any suitable method (or combination of methods)including, for example, blanket dry (plasma) etch-back or CMPprocessing, thereby leaving only those portions of the photoresistbuffer layer 14 and the conductive material layers 7, 8 that were in theremaining portion of the opening 6.

As illustrated in FIG. 2F, the remaining portions of the molding layer 4can then be removed with an appropriate etch, for example, a wet etchusing a LAL etch composition, while the lower portion 14 b of thephotoresist buffer layer 14 serves as an etch mask to protect the lowerportions of the conductive material layers 7, 8 and the underlyingconductive region 2. As illustrated in FIG. 2G, the lower portion 14 bof the photoresist buffer layer 14 may then be removed with aconventional ashing process during which the organic photoresist isexposed to a combination of elevated temperatures and/or activatedoxygen species in order to “burn” the lower portion 14 b of the resistout of the opening 6. The “ashed” substrate is then typically subjectedto a clean-up process to remove residual photoresist and/or particulatecontamination before the subsequent processing necessary to complete thecapacitor structure.

This second conventional method, therefore, by reducing the likelihoodof voids within the buffer material provided within the opening 6,improves the degree of protection afforded the conductive materiallayers 7, 8 from the etch composition(s) being used to remove themolding layer 4, thereby reducing the possibility that one or more ofthe layers will be damaged, contaminated or breached.

The conventional novolak photoresist compositions typically includethree basic ingredients, specifically 1) a phenolic novolak resin, 2) adiazonaphthoquinone (DNQ) type dissolution inhibitor, and 3) an organicsolvent. The novolak resin is utilized primarily for establishing thebasic physical properties of the resulting photoresist film, forexample, good film forming characteristics, etch resistance and thermalstability. The DNQ component, however, is utilized for modifying therelative dissolution rate of the exposed and unexposed regions of thenovolak photoresist film in conventional alkaline developing solutionsand allowing a useful photoresist pattern to be developed from theexposed photoresist film. The organic solvent(s) included in thephotoresist composition are selected to provide appropriate viscositycontrol for the photoresist composition to allow the production ofuniform, glassy thin photoresist films by, for example, spin coatingtechniques.

Novolak resins are soluble in a variety of common organic solventsincluding, for example, cyclohexanone, acetone, ethyl lactate, NMP(1-methyl-2-pyrrolidinone), diglyme (diethyleneglycol dimethyl ether),and PGMEA (propyleneglycol methyl ether acetate). Commercialphotoresists are generally Formulated with polymer loadings of 15 to 30weight percent with respect to the solvent content of the resistcomposition with the viscosity of the solution being adjusted by varyingthe polymer to solvent ratio of the composition, thereby allowingdifferent photoresist compositions to be Formulated for generating avariety of film thicknesses.

The addition of DNQ inhibitors to novolak resins retards the dissolutionrate of the photoresist film with an increasing concentration of the DNQinhibitor(s) tending to further retard the dissolution rate. Uponexposure to radiation of appropriate frequency and intensity, however,the DNQ-novolak composition will tend to exhibit a dissolution rategreater than the dissolution rate of pure novolak resin. ConventionalDNQ-novolak resists may have a DNQ inhibitor content of approximately 20weight percent with respect to the weight of novolak resin, and canprovide a differential dissolution rate of more than three orders ofmagnitude between the unexposed and exposed states. The nature of theinteraction between the DNQ dissolution inhibitors and novolak resins iscomplex, but experimental evidence has suggested that hydrogen bondingof the inhibitor to the novolak resin plays an important role ininhibiting dissolution of the composition.

The developing solutions used for developing DNQ-novolak photoresistcompositions are generally aqueous alkaline solutions. Although theearliest developing solutions used with DNQ-novolak resists were alkalimetal hydroxide solutions, for example, dilute KOH or NaOH solutions, asthe semiconductor industry has become more sensitive to metalcontamination, the use of these metal containing developing solutionshas decreased in favor of organic developers, for example, aqueoussolutions of tetramethyl ammonium hydroxide (TMAH), typically at aconcentration of between 0.2 and 0.3N.

The basic novolak resins include repeating phenol derivative monomerunits that may be represented by, for example, the Formula:

and may, in other instances, form complexes with the DNQ inhibitorcompounds, for example, derivatives of 4- and 5-DNQ sulfonyl chlorides,with may be represented by, for example, the Formula (where r is ahalogen):

After the novolak photoresists have been developed and baked orotherwise cured or hardened, the residual portions of the photoresistfilm may be difficult to remove using conventional ashing processes,thereby increasing the processing time and expense and increasing thelikelihood of incomplete removal that could compromise subsequentprocessing, functional yield and/or the reliability of the resultingdevices. Without being bound by theory, it is believed that theprevalence of the C═C bonds in the phenol derivative backbone of thenovolak polymer accounts for the film's resistance to conventionalashing processes.

As detailed above, the use of conventional inorganic materials forforming buffer layers, for example, silicon oxides that are formed byone or more CVD processes, tend to exhibit increasing void formation asthe aspect ratio (depth/width) of the openings increases. See FIGS.1A-1E and the corresponding description provided above. The use ofconventional inorganic layers will also tend to increase the processingtime as a result of the etch back and/or CMP processes necessary toremove the upper portion of the layers.

As also detailed above, the use of conventional novolak-basedphotoresist compositions for forming buffer layers requires the use ofan exposure step in order to breakdown the polymers in the photoresistcomposition and/or modify their solubility to a degree that will allowthem to be removed during a subsequent developing step. See FIGS. 2A-2Gand the corresponding description provided above. Conventionalnovolak-based photoresist compositions are also typically subjected to arelatively high bake temperature on the order of 270° C. in order toharden the photoresist so that it is better suited to endure wet etchsolutions without excessive dissolution and contamination of the wetetch bath equipment by the dissolving photoresist layer. This exposurestep and the subsequent baking step will both involve additionalhandling, equipment and processing time, all of which will tend toincrease the overall processing cost, the risk of handling induceddamage and the overall processing time.

BRIEF SUMMARY OF THE INVENTION

As discussed above, the invention is directed to particular polymercompositions, photoresist compositions incorporating such polymercompositions and methods of fabricating semiconductor devices utilizingsuch photoresist and/or polymer compositions as a buffer layer. Theinvention is also directed to polymer compositions that, when used toform a buffer layer or pattern, can be more easily removed from thesurface of a semiconductor substrate, thereby increasing productivityand/or reducing the likelihood of defects and failures associated withresidual photoresist material.

Polymer compositions according to example embodiments of the inventioninclude copolymers comprising from 61 to 75 weight percent benzylmethacrylate and from 8 to 15 weight percent alkyl acrylic acid with thebalance being hydroxy alkyl methacrylate, including compositions inwhich the hydroxy alkyl methacrylate accounts for 17 to 24 weightpercent. Polymer compositions according to example embodiments of theinvention include copolymers having a mean molecular weight from 6700 to7500 and a number mean molecular weight of 2600 to 3200. As suggestedabove, polymer compositions according to example embodiments of theinvention include copolymers having at least three monomers and has astructure corresponding to Formula I below:

wherein the variables L, M and N represent the relative molar fractionsof the monomers and satisfy the expressions 0<L≦0.8; 0<M≦0.2; 0<L≦0.35;and L+M+N=1 and further wherein R¹, R² and R³ are independently selectedfrom lower alkyls, e.g., C₁-C₆ alkyls, and particularly the C₁-C₄ alkylsand derivatives thereof.

The polymer compositions according to example embodiments of theinvention include copolymers having a structure corresponding to FormulaI wherein the variables L and M also satisfy the expressions0.45≦L≦0.65; and 0.15≦M≦0.25. The polymer compositions according toexample embodiments of the invention also include copolymers having astructure corresponding to Formula I wherein the variables L, M and Nsatisfy the expressions 0.45≦L≦0.65; 0.15≦M≦0.25 and 0.20≦N≦0.27. Thepolymer compositions according to example embodiments of the inventionalso include copolymers having a structure corresponding to Formula Iwherein the variables L, M and N satisfy the expressions 0.45≦L≦0.65;0.15≦M≦0.25 and 0.17≦N≦0.25. The polymer compositions according toexample embodiments of the invention also include copolymers having astructure corresponding to Formula I wherein the variables L, M and Nsatisfy the expressions 0.45≦L≦0.65 and 0.17≦M≦0.25.

The polymer compositions according to example embodiments of theinvention also include copolymers having a structure wherein the alkylacrylic acid is selected from a group of consisting of the C₁-C₄ acrylicacids and mixtures thereof and the hydroxy alkyl methacrylate isselected from a group of consisting of the C₁-C₄ hydroxy alkylmethacrylates and mixtures thereof. The polymer compositions accordingto example embodiments of the invention also include copolymers having astructure wherein the alkyl acrylic acid includes a major portion ofmethyl acrylic acid and the hydroxy alkyl methacrylate includes a majorportion of hydroxy ethyl methacrylate and those polymer compositions inwhich the alkyl acrylic acid consists essentially of methyl acrylic acidand the hydroxy alkyl methacrylate consists essentially of hydroxy ethylmethacrylate.

Example embodiments of the invention also encompass node separationpolymer compositions comprising a copolymer having from 61 to 75 weightpercent benzyl methacrylate and from 8 to 15 weight percent alkylacrylic acid with the balance of the copolymer being hydroxy alkylmethacrylate; a cross-linking agent; a thermal acid generator; asurfactant; and a solvent. Example embodiments of the node separationpolymer compositions also include those in which the copolymer has amean molecular weight of 6700 to 7500, those in which the alkyl acrylicacid is selected from a group of consisting of the C₁-C₄ acrylic acidsand mixtures thereof and the hydroxy alkyl methacrylate is selected froma group of consisting of the C₁-C₄ hydroxy alkyl methacrylates andmixtures thereof, those in which the alkyl acrylic acid includes a majorportion of methyl acrylic acid and the hydroxy alkyl methacrylateincludes a major portion of hydroxy ethyl methacrylate, and those inwhich the alkyl acrylic acid consists essentially of methyl acrylic acidand the hydroxy alkyl methacrylate consists essentially of hydroxy ethylmethacrylate.

Although those skilled in the art will appreciate that a variety ofsolvents or solvent systems may be incorporated in the node separationpolymer compositions, it is expected that solvents selected from a groupconsisting of propylene glycol methyl ether, propylene glycol monomethyl ether acetate, ethylene glycol methyl ether, ethylene glycolmethyl ether acetate, ethyl lactate, γ-butyrolactone, ethyl3-ethoxypropionate, N-methyl-2-pyrrolidinone, dimethyl formamide,dimethyl acetamide, diethyl acetamide, dimethylsulfoxide, acetonitrile,carbitol acetate, dimethyl adipate or sulfolane and mixtures thereofwill provide acceptable performance in most instances.

Example embodiments of the invention also encompass methods forprotecting recessed regions comprising forming an insulating layer on asemiconductor substrate; forming an opening in the insulating layer;forming a protected layer on an upper surface of the insulating layerand a lower surface and sidewalls of the opening; forming a buffer layeron the protected layer, the buffer layer filling the recess andincluding a major portion of a copolymer having from 61 to 75 weightpercent benzyl methacrylate; from 8 to 15 weight percent alkyl acrylicacid; with a balance being hydroxy alkyl methacrylate; removing an upperportion of the buffer layer using a developer solution to expose anupper portion of the protected layer, a remaining portion of the bufferlayer substantially filling the recess; and removing the upper portionof the protected layer while a lower portion of the protect layer isprotected by the remaining portion of the buffer layer. In some exampleembodiments of the method of protecting the balance of the copolymer mayconstitute from 17 to 24 weight percent. The copolymers according toexample embodiments of the invention may have a mean molecular weightof, for example, 6700 to 7500 or, in another example embodiment, 6900 to7200 and/or may have a number mean molecular weight of 2600 to 3200 or,in another embodiment 2800 to 3100. The polymers according to theexample embodiments of the invention will be formed from at least threemonomers that may be represented by the structure illustrated in FormulaI above wherein the variables L, M and N represent the relative molarfractions of the monomers and satisfy the expressions 0<L≦0.8; 0<M≦0.2;0<L≦0.35; and L+M+N=1 and wherein R¹, R² and R³ are independentlyselected from C₁-C₄ alkyls and their derivatives. In some exampleembodiments the variables may also satisfy the expressions 0.45≦L≦0.65and 0.15≦M≦0.25 and, in some instances 0.20≦N≦0.27.

Additional example embodiments may utilize combinations that satisfyother expressions including, for example, 0.17≦M≦0.25, include alkylacrylic acids selected from a group of consisting of the C₁-C₄ acrylicacids and mixtures thereof; and/or hydroxy alkyl methacrylates selectedfrom a group of consisting of the C₁-C₄ hydroxy alkyl methacrylates andmixtures thereof. Indeed, it is anticipated that methods according tothese example embodiments of the invention may be practiced with any ofthe polymers and/or photoresist compositions described above.

As detailed below, example embodiments of the invention include methodsof forming capacitors comprising forming an insulating layer on asemiconductor substrate; forming an opening in the insulating layer;forming a conductive layer on an upper surface of the insulating layerand a lower surface and sidewalls of the opening; forming a buffer layeron the conductive layer, the buffer layer filling the recess andincluding a major portion of a copolymer having from 61 to 75 weightpercent benzyl methacrylate; from 8 to 15 weight percent alkyl acrylicacid; and with the balance of the copolymer being hydroxy alkylmethacrylate; removing an upper portion of the buffer layer using adeveloper solution to expose an upper portion of the conductive layer, aremaining portion of the buffer layer substantially filling the recess;and removing the upper portion of the conductive layer to separate lowerelectrode structures; removing the remaining portion of the bufferlayer; forming a dielectric layer on the lower electrode structures; andforming an upper electrode on the dielectric layer. Again, it isanticipated that methods according to these example embodiments of theinvention may be practiced with any of the polymers and/or photoresistcompositions described above.

Example embodiments of the invention include methods of formingsemiconductor devices comprising forming an electric element on asemiconductor substrate; forming an insulating layer on the electricelement; forming an opening in the insulating layer to expose a contactregion on the electric element; forming a conductive layer on an uppersurface of the insulating layer and a lower surface and sidewalls of theopening; forming a buffer layer on the conductive layer, the bufferlayer filling the recess and including a major portion of a copolymerhaving from 61 to 75 weight percent benzyl methacrylate; from 8 to 15weight percent alkyl acrylic acid and with the balance or remainder ofthe copolymer being hydroxy alkyl methacrylate; removing an upperportion of the buffer layer using a developer solution to expose anupper portion of the conductive layer, a remaining portion of the bufferlayer substantially filling the recess; removing the upper portion ofthe conductive layer to separate lower electrode structures; removingthe remaining portion of the buffer layer; forming a dielectric layer onthe lower electrode structures; and forming an upper electrode on thedielectric layer.

Developing solutions may be tailored to some degree to provide thedesired dissolution rate, for example, an aqueous developer solutionincluding from 1 to 5 wt % TMAH. The developing solution(s) may then beutilized for removing the upper portion of the buffer layer using adeveloper solution that maintains an average photoresist removal rate ofat least 30 Å/second. When conventional ashing equipment and proceduresare applied to a photoresist composition consistent with the inventiondescribed below, increased photoresist removal rates may be obtainedrelative to that experienced with conventional novolak-basedphotoresists. For example, compositions according to example embodimentsof the invention may be removed at average removal rates of at least 150Å/second or about five times the rate exhibited by conventionalphotoresist compositions under the same conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more apparent by describing in detail exampleembodiments thereof with reference to the attached drawings in which:

FIGS. 1A through 1E are cross-sectional views illustrating aconventional method of forming an OCS-type capacitor electrode using anoxide buffer layer;

FIGS. 2A through 2G are cross-sectional views illustrating aconventional method of forming an OCS-type capacitor electrode using aconventional novolak-based photoresist to form a buffer layer;

FIGS. 3A through 3F are cross-sectional views illustrating a method offorming an OCS-type capacitor electrode using a polymer resincomposition and a method according to example embodiments of theinvention;

FIGS. 4A through 4J are cross-sectional views illustrating a method offorming a semiconductor device that includes an OCS-type capacitor usinga polymer resin composition and a method according to exampleembodiments of the invention;

FIG. 5 illustrates a cross-sectional SEM image of lower electrodes thatwere fabricated using a polymer resin composition and a method accordingto example embodiments after the buffer layer has been removed byashing; and

FIG. 6 illustrates a top-view SEM image of lower electrodes that werefabricated using a polymer resin composition and a method according toexample embodiments after the buffer layer has been removed by ashing.

These drawings have been provided to assist in the understanding of theexample embodiments of the invention as described in more detail belowand should not be construed as unduly limiting the invention. Inparticular, the relative spacing, positioning, sizing and dimensions ofthe various elements illustrated in the drawings are not drawn to scaleand may have been exaggerated, reduced or otherwise modified for thepurpose of improved clarity.

Those of ordinary skill will appreciate that certain of the variousmonomers, polymers, barrier coating compositions and barrier coatingprocesses as illustrated or described with respect to the exampleembodiments may be selectively and independently modified and/orcombined to create other monomers, polymers, barrier coatingcompositions and barrier coating processes useful for manufacturingsemiconductor devices without departing from the scope and spirit ofthis disclosure.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Polymers according to the example embodiments of the invention may begenerally represented by Formula I below:

wherein the variables L, M and N represent the relative molar fractionsof the monomers and satisfy the expressions 0<L≦0.8; 0<M≦0.2; 0<L≦0.35;and L+M+N=1 and further wherein R¹, R² and R³ are independently selectedfrom lower alkyls, e.g., C₁-C₆ alkyls, and particularly the C₁-C₄alkyls, and derivatives thereof. The polymers according to the exampleembodiments of the invention will also exhibit a polystyrene conversionweight mean molecular weight of 6700 to 7500 and a number mean molecularweight of 2600 to 3200.

An example embodiment of a polymer including three monomers, i.e., aterpolymer, according to the invention is represented by the Formula IIbelow:

wherein the variables L, M and N again represent the relative molarfractions of the monomers and satisfy the expressions 0<L≦0.8; 0<M≦0.2;0<L≦0.35; and L+M+N=1 and further wherein R¹, R² and R³ are propyl,methyl and ethyl groups respectively.

Polymers according to the example embodiments of the invention may, inturn, be utilized in combination with other components, for example, oneor more solvents, activators, inhibitors and/or viscosity modifiers toform polymer resin compositions according to other example embodimentsof the invention. As will be addressed in more detail below, thedissolution rate of the polymer resin compositions according to theexample embodiments of the invention tends to correlate to theproportion of the acrylic acid monomer incorporated in the polymer.Polymer resin compositions including as a primary component a polymeraccording to the example embodiments of the invention in which theproportion of the acrylic acid monomer is lower will tend to exhibit acorrespondingly lower dissolution rate. For example, polymer resincompositions including less than 8 weight percent (all weight percentsare with respect to the total weight of the polymer) methyl acrylic acidtend to exhibit dissolution rates of less than 30 Å/second while similarpolymer resin compositions including at least 15 weight percent methylacrylic acid tend to exhibit dissolution rates of at least 1000Å/second.

A polymer according to the example embodiments of the invention, forexample, as represented above in Formula II, may be polymerized from amixture including 61 to 75 weight percent of a benzyl methacrylatemonomer, 8 to 15 weight percent of a methyl acrylic acid monomer, forexample, between 10 and 13 weight percent, and 17 to 24 weight percentof a hydroxy ethyl methacrylate monomer.

As will be appreciated, the relative weight percentages of the variousclasses of monomers may be adjusted as needed to satisfy themathematical expressions noted above with respect to Formula I.Similarly, as will be appreciated, polymers according to the exampleembodiments of the invention may include more than one monomer from aparticular class, for example, a mixture of hydroxy ethyl methacrylateand hydroxy propyl methacrylate monomers may be used as long as thevarious limitations and relationships noted above with respect to R³ andN are still satisfied. Such combinations of closely related monomers maybe useful for “fine-tuning” the performance of a polymer resincomposition incorporating such polymers, for example, the dissolutionrate of a layer formed from such a polymer resin composition.

As noted above, one or more polymers according to the exampleembodiments of the invention will typically be incorporated in polymerresin compositions according to other example embodiments of theinvention for use in fabricating semiconductor devices. In suchinstances, the polymer(s) according to Formula I will typically compriseat least 50, and may exceed 90, weight percent of the polymer resincomposition. Other components of the polymer resin composition willtypically include 1 to 7 weight percent (typically 1.5 to 5 weightpercent) of one or more cross-linking agents, for example, a melamineresin, 0.01 to 0.5 weight percent of one or more thermal acid generators(typically 0.03 to 0.2 weight percent), for example, paratoluenesulfonic acid pyridine salt, pyridine and mixtures thereof. Thecross-linker and the thermal acid generator components act as agents forcross-bonding copolymers during a thermal process, i.e., baking process,used to harden the buffer layer. The polymer resin compositionsaccording to example embodiments of the invention will also typicallyinclude 0.01 to 1 weight percent of one or more surfactants (typically0.1 to 0.6 weight percent). The balance of the polymer resin compositionwill, in turn, be made up of an appropriate solvent or solvent system.

A variety of solvents may be utilized in the polymer resin compositionincluding, for example, combination with other components, for example,one or more of propylene glycol methyl ether, propylene glycol monomethyl ether acetate, ethylene glycol methyl ether, ethylene glycolmethyl ether acetate, ethyl lactate, γ-butyrolactone, ethyl3-ethoxypropionate, N-methyl-2-pyrrolidinone, dimethyl formamide,dimethyl acetamide, diethyl acetamide, dimethylsulfoxide, acetonitrile,carbitol acetate, dimethyl adipate or sulfolane and mixtures thereof.

The polymer resin compositions according to the invention may coated ona substrate and then subjected to a low (or soft) bake (or curing) at nomore than about 200° C. to form a buffer layer without requiring anexposure step as in the conventional processes for forming a bufferlayer using photoresist. By controlling the relative fraction of thepolymer attributed to the acrylic acid monomer(s), polymer resincompositions according to example embodiments of the invention can beprovided with a dissolution rate that is controlled to be within atarget range. Further, polymer resin compositions according to exampleembodiments of the invention will also tend to exhibit an increasedremoval rate under ashing relative to that achieved by conventionalphotoresists under identical or substantially identical conditions.Polymer resin compositions according to example embodiments of theinvention will also tend to exhibit decreased solubility in solventscommonly used during semiconductor fabrication, for example, IPA and LALsolutions.

Polymer resin compositions according to example embodiments of theinvention may be used to form buffer layers during the fabrication ofOCS-type lower electrodes as illustrated in FIGS. 3A-3F. As illustratedin FIG. 3A, an oxide layer, specifically a mold oxide layer 110 isformed on a substrate 100. The mold oxide layer 110 is then patternedand etched to form an mold oxide pattern including opening 112 throughwhich a portion of the surface of the substrate 100 is exposed.

As illustrated in FIG. 3A, a conductive layer 115 is then formed on themold oxide pattern, including the sidewalls that define the opening 112and the exposed surface of the substrate 100. The conductive layer 115typically comprises at least one material selected from a groupconsisting of polysilicon, tungsten (W), titanium (Ti), titanium nitride(TiN) and tungsten nitride (WiN). For example, a multi-layer conductivelayer 115 may be formed using a layer of a metal and a layer of thecorresponding metal nitride to provide barrier layer and/or adhesionlayer functionality, for example, a Ti/TiN stacked structure.

As illustrated in FIG. 3C, a buffer layer 130 is then formed using apolymer resin composition that is deposited to a thickness and underconditions sufficient to fill the opening 112 with the polymer resincomposition and form an additional layer of the polymer resincomposition across the exposed surface of the mold oxide pattern. Thebuffer oxide layer includes both an upper buffer layer region 126 and alower buffer layer region 124. The buffer layer may be formed using anysuitable application technique including, for example, conventional spincoating methods.

As illustrated in FIG. 3D, the upper buffer layer region 126 is then isremoved using a conventional developing solution, for example, anaqueous solution of TMAH (tetramethyl ammonia hydroxide, typically at aconcentration of 1.5 to 4 weight percent) with the balance of thesolution being water and, optionally, additives such as pH adjuster(s),surfactant(s) and buffering agents. The remaining portion of the bufferlayer, the lower buffer layer region 124 is then hardened by heatingtreatment (curing or baking) at a bake temperature of 150 to 200° C. fora period sufficient to form a hardened buffer layer pattern 125 bycross-bonding the copolymers in the polymer resin.

This hardened buffer layer pattern 125 will serve to protect theconductive layer 115 from damage during the conductive layer patterningstep as depicted in FIG. 3E. In other words, the hardened buffer layerpattern 125 will not readily dissolve in solvents and wet etchcompositions commonly found in a semiconductor processing environmentincluding, for example, LAL solutions, isopropyl alcohol (IPA) andwater.

A conductive pattern 116 is then formed by removing the upper portion ofthe conductive layer 115, particularly that portion of the conductivelayer 115 found on the upper surface of the mold oxide pattern. Theupper portion of the conductive layer 115 may be removed using anappropriate blanket etch using the hardened buffer layer pattern 125 asa etch mask or by using a conventional CMP process. As the upper surfaceof the mold oxide pattern is exposed the conductive pattern 116 isformed from the portions of the conductive layer 115 remaining in theopenings 112. After removing the upper portion of the conductive layer115, the substrate may be subjected to a cleaning step to remove etchresidue and/or other debris from the exposed surfaces involving, forexample, IPA and/or D.I. water.

The mold oxide pattern can then be removed using a conventional wet etchmethod, for example, using a LAL solution (water, HF and ammoniumfluoride (NH₄F)), again using the hardened buffer pattern 125 as an etchmask to protect the conductive pattern 116 formed in the opening 112.The hardened buffer layer 125 can then be removed in an ashing stepusing an O₂ plasma method.

Without being bound by theory, it is believed that the buffer layersformed using a polymer resin composition according to the exampleembodiments of the invention are cross-bonded and includes a ring shapedhydrocarbon compound that comprises only about 5 to 20 weight percent ofthe resin composition. It is believed that this result is achieved byforming the hardened buffer layer 125 having a predominatelymethacrylate structure. Accordingly, and again without intending to bebound by speculation regarding the precise mechanism, it is believedthat the hardened buffer layer 125 exhibits an enhanced etch rate (ormaterial removal rate) under a conventional ashing process relative to aconventional photoresist, specifically photoresists based on novolakresin(s), that can be attributed to the reduction in the double bondsfound in the base polymer. The ratio of the material removal rates forpolymer resin compositions according to example embodiments of theinvention and the material removal rates for conventional novolak resinbased photoresists has been observed as being in the range of about 6:1.

Polymer resin compositions according to example embodiments of theinvention may be used to form buffer layers during the fabrication ofsemiconductor devices, for example, DRAMs, that include OCS-type lowerelectrodes as illustrated in FIGS. 4A-4J. As illustrated in FIGS. 4A and4B, the semiconductor manufacturing process may remain conventionalthrough the formation of active regions in a semiconductor substrate 200using a shallow trench isolation pattern 205. Source regions 235 anddrain regions 240 may then be formed in the active regions adjacent gatestructures including a gate dielectric layer, a gate electrode 230 andgate spacers 225 adjacent opposite sides of the gate electrode. A firstdielectric layer 245 can then be formed on the gate structures and afirst pad pattern 250, 255 provided for establishing electrical contactto the source/drain regions 235, 240 respectively. A second dielectriclayer 260 can then be formed and a bit line 270 formed in a contact hole265 opened in the second dielectric layer 260 to provide electricalcontact to the drain region 240 through the first pad pattern 250, 255.A third dielectric layer 275 can then be formed over the bit line 270through which a second pad pattern 280 can be formed to provideelectrical contact to the source regions 235.

As illustrated in FIG. 4C, an etch stop layer 305 is then formed on thesecond pad pattern 280 and the exposed upper surface of the thirddielectric layer 275. The etch stop layer 305 protects the second padpattern 280 during the selective etch step used for etching the moldoxide layer to form the mold oxide pattern 310. The etch stop layer 305typically comprises a nitride material or a metal oxide having athickness sufficient to protect the underlying material from the oxideetch, for example, 10 to 200 Å, depending on the combination of thematerial, the etch chemistry and the relative thickness of the materialsbeing etched and protected respectively.

As illustrated in FIG. 4C, the mold oxide pattern 310 includes openings312 that may be formed using a conventional photolithographic processsequence of forming a resist pattern and then using that pattern as anetch mask during the subsequent oxide etch process. A portion of theetch stop layer 305 will be exposed by the opening 312 and may beremoved using the oxide etch or by using an etch chemistry more suitedto the material used to form the etch stop layer. When the exposedportion of the etch stop layer 305 is removed an upper surface of thesecond pad pattern 280 and, in this instance, a portion of thesurrounding third dielectric layer 275.

As illustrated in FIG. 4D, a conductive layer 315 that will be used toform a bottom electrode is formed on the mold oxide pattern 310including all of the surfaces exposed within the opening 312. Theconductive layer 315 may have a multi-layer structure including, forexample, a stacked structure of titanium and titanium nitride films,having a thickness in the range of about 200 to 500 Å.

As illustrated in FIG. 4E, a buffer layer 330 may be formed on theconductive layer 315, using a polymer resin composition according toexample embodiments of the invention, to a thickness sufficient to fillthe opening 312. An upper portion 326 of the buffer layer 330 can thenbe removed from the substrate using a conventional developing solutioncomprising an aqueous tetramethyl ammonia hydroxide solution (typically1.5 to 4 weight percent TMAH, for example 2.4 weight percent), leavingonly the lower portion 324 of the buffer layer 330 on the substrate. Thepolymer(s) according to example embodiments of the invention remainingin the lower portion 324 of the buffer layer 330 is then cross-linkedusing a heat treatment (also referred to as a curing or bake step) atabout 150 to 200° C. to harden the lower portion of the buffer layer asillustrated in FIG. 4F.

As illustrated in FIG. 4G, the upper portion of the conductive layer 315is removed from the substrate using, for example, a conventional dryetch back process or CMP method to expose the top surface of the moldoxide pattern 310 and form a cylindrically-shaped bottom electrode 320.The substrate may then be cleaned to remove any etch residue remainingon the mold oxide pattern 310, the hardened buffer layer 325 or thebottom electrode 320. Conventional cleaning processes may use acombination of IPA or deionized (D.I.) water.

As illustrated in FIG. 4H, the mold oxide pattern 310 is then removedusing, for example, a wet etch method using a LAL etch solutionconsisting of water, hydrogen fluoride and ammonium fluoride. Thehardened buffer layer 325 may then be removed by ashing the substrateusing an O₂ plasma to form the bottom electrode of the capacitor asillustrated in FIG. 4I. As noted above, the ashing duration necessary toclean the residual portions of the polymer resin composition issignificantly less than that required for conventional photoresist,e.g., novolak resin based photoresists, removal, for example, an ashingtime that is about 16-17% of that required for conventional photoresistcompositions. As illustrated in FIG. 4J, a capacitor dielectric 340 andan upper electrode 350 can then be formed over the lower electrode 320to complete the capacitor structure.

Example Embodiments of Polymers Polymer—Example 1

A first polymer composition according to example embodiments of theinvention was prepared by combining propylene glycol mono methyl etheracetate: 501.4 g, benzyl methacrylate: 152 g; 2-hydroxy ethyl acrylate:43.7 g; methyl acrylic acid: 22.96 g; anddimethyl-2,2′-azobis(2-methylpropionate: 40.5 g.

This mixture was then reacted for 1-3 hours at 80° C., and thenapparently stirred for 4-5 hours, to obtain a polymer having apolystyrene conversion weight mean molecular weight of 7100 and a numbermean molecular weight of 2900. The methyl acrylic acid content of thecopolymer was 10.5 weight percent.

Polymer—Example 2

A second polymer according to example embodiments of the invention wasprepared by combining propylene glycol mono methyl ether acetate: 501.4g, benzyl methacrylate: 150.9 g, 2-hydroxy ethyl acrylate: 43.7 g,methyl acrylic acid: 24.1 g, dimethyl-2,2′-azobis(2-methylpropionate):40.5 g.

The mixture was then reacted for 1-3 hours at 80° C. and then stirredfor 4-5 hours, to obtain a polymer exhibiting a polystyrene conversionweight mean molecular weight of 7000, a number mean molecular weight of2900, and the methyl acrylic acid content of the copolymer was 11 weightpercent.

Polymer—Example 3

A third polymer according to example embodiments of the invention wasprepared by combining propylene glycol mono methyl ether acetate: 501.4g; benzyl methacrylate: 149.8 g; 2-hydroxy ethyl acrylate: 43.7 g;methyl acrylic acid: 25.1 g, α-methylstyrene dimer: 25.15 g; anddimethyl-2,2′-azobis(2-methylpropionate: 40.5 g.

This mixture was then treated for 1 to 3 hours at 80° C. and stirred for4 to 5 hours to obtain a copolymer having a polystyrene conversionweight mean molecular weight of 7000 and a number mean molecular weightof 2900. The methyl acrylic acid content of the copolymer was 11.5weight percent.

Polymer—Example 4

A fourth polymer according to example embodiments of the invention wasprepared by combining propylene glycol mono methyl ether acetate: 501.4g; benzyl methacrylate: 152 g; 2-hydroxy ethyl acrylate: 43.7 g; methylacrylic acid: 21.74 g, α-methylstyrene dimer: 25.15 g; anddimethyl-2,2′-azobis(2-methylpropionate: 40.5 g.

This mixture was then treated for 1 to 3 hours at 80° C. and stirred for4 to 5 hours to obtain a copolymer having a polystyrene conversionweight mean molecular weight of 7100 and a number mean molecular weightof 2900. The methyl acrylic acid content of the copolymer was 10 weightpercent.

Polymer—Example 5

A fifth polymer according to example embodiments of the invention wasprepared by combining propylene glycol mono methyl ether acetate: 501.4g; benzyl methacrylate: 149.8 g; 2-hydroxy ethyl acrylate: 43.7 g;methyl acrylic acid: 26.7 g, α-methylstyrene dimer: 25.15 g; anddimethyl-2,2′-azobis(2-methylpropionate: 40.5 g.

This mixture was then reacted for 1-3 hours at 80° C. and stirred for4-5 hours to obtain a copolymer having a polystyrene conversion weightmean molecular weight of 7050 and a number mean molecular weight of2850. The methyl acrylic acid content of the copolymer was 12 weightpercent.

Example Embodiments of Polymer Resin Compositions Node SeparationPolymer—Example 6

A node separation polymer (NSP) according to example embodiments of theinvention was prepared by combining the copolymer prepared in Example 1:1:83 g; melamine resin: 2.88 g; paratoluene sulfonic acid pyridine salt:0.04 g; pyridine: 0.04 g; surfactant: 0.28 g; propylene glycol monomethyl ether acetate: 10.05 g.

Node Separation Polymer—Example 7

A node separation polymer (NSP) according to example embodiments of theinvention was prepared by combining the copolymer prepared in Example 2:42 g; melamine type resin: 2.88 g; paratoluene sulfonic acid pyridinesalt: 0.04 g; pyridine: 0.04 g; surfactant: 0.28 g; and propylene glycolmono methyl ether acetate: 10.05 g.

Node Separation Polymer—Example 8

A node separation polymer (NSP) according to example embodiments of theinvention was prepared by combining the copolymer prepared in Example 2:83 g; melamine type resin: 2.88 g; paratoluene sulfonic acid pyridinesalt: 0.04 g; pyridine: 0.04 g; surfactant: 0.28 g; propylene glycolmono methyl ether acetate: 10.05 g.

Node Separation Polymer—Example 9

A node separation polymer (NSP) according to example embodiments of theinvention was prepared by combining the copolymer prepared in Example 2:42 g, copolymer of the composition example 3: 42 g; melamine resin: 2.88g; paratoluene sulfonic acid pyridine salt: 0.04 g; pyridine: 0.04 g;surfactant: 0.28 g, propylene glycol mono methyl ether acetate: 10.05 g.

Node Separation Polymer—Example 10

A node separation polymer (NSP) according to example embodiments of theinvention was prepared by combining the copolymer prepared in Example 3:83 g; melamine resin: 2.88 g; paratoluene sulfonic acid pyridine salt:0.04 g; pyridine: 0.04 g; surfactant: 0.28 g; and propylene glycol monomethyl ether acetate: 10.05 g.

Node Separation Polymer—Example 11

A node separation polymer (NSP) according to example embodiments of theinvention was prepared by combining the copolymer prepared in Example 4:83 g; melamine resin: 2.88 g; paratoluene sulfonic acid pyridine salt:0.04 g; pyridine: 0.04 g; surfactant: 0.28 g; and propylene glycol monomethyl ether acetate: 10.05 g.

Node Separation Polymer—Example 12

A node separation polymer (NSP) according to example embodiments of theinvention was prepared by combining the copolymer prepared in Example 5:83 g, melamine resin: 2.88 g; paratoluene sulfonic acid pyridine salt:0.04 g; pyridine: 0.04 g; surfactant: 0.28 g; propylene glycol monomethyl ether acetate: 10.05 g.

Node Separation Polymer Comparative Example 1

A comparative example was prepared using a phenol novolak resin: 25 g,melamine resin: 2.88 g; paratoluene sulfonic acid pyridine salt: 0.04 g;pyridine: 0.04 g; surfactant: 0.28 g; propylene glycol mono methyl etheracetate: 68.05 g.

Using certain of the example embodiments of the invention previouslyproduced, a series of tests were conducted to evaluate the performanceand significance of the polymers and compositions described above.

Dissolution Rate Evaluation of Polymer Resin According to MAA Content

The significance of the acrylic acid component to the dissolution rateof the resulting polymer resin compositions was then evaluated usingvarious of the node separation polymers. Substrates were coated and then“developed” using the same developing composition in order to comparethe relative performance of the two competing polymers. The results ofthis evaluation are reflected below in TABLE 1.

TABLE 1 Methyl Acrylic Acid (wt %) 10% 11% 12% Dissolution Rate 37.7Å/sec 283.2 Å/sec 774.6 Å/sec

As reflected in the data above, the polymer resin compositions accordingto example embodiments of the invention reflect a strong dependence onthe concentration of MAA present within the film. For example, a 20%increase in the relative MAA concentration from 10% to 12% translatedinto a 20× increase in the dissolution rate for the composition havingthe higher MAA concentration.

Evaluation of Dissolution Rates Re MAA Concentration

The significance of the acrylic acid component to the dissolution rateof the resulting polymer resin compositions was further evaluated usingvarious of the node separation polymers. Substrates were coated and then“developed” using the same developing composition in order to comparethe relative performance of the two competing polymers with respect tonode separation polymers. The results of this evaluation are reflectedbelow in TABLE 2.

TABLE 2 Ex. 1 Ex. 3 Ex. 5 Ex. 6 Ex. 7 MAA (wt %) 10.5% 11% 11.5% 10% 12%Buffer layer removed 6270 Å 11330 Å 20555 Å 1429 Å 30895 Å DissolutionRate 157 (Å/S) 283 (Å/S) 514 (Å/S) 35 (Å/S) 772 (Å/S)

The polymer resin buffer layers according to experimental example 1, 3,5-7 are respectively coated on the mold oxide pattern that included anumber of openings in the substrate to a thickness of about 45,000 Å.After measuring, these buffer layers were then exposed to a developingsolution including 2.4 weight percent of TMAH for about 40 seconds. Theremaining portion of the polymer resist composition was then measured todetermine how much of the original layer had be removed or scrambled.

Solubility Evaluation of Example Buffer Layers

TABLE 3 Polymer resin Ex. Ex. Ex. Ex. Ex. Ex. Ex. Comparativecomposition 1 2 3 4 5 6 7 example Surface uniformity & N N N N N N N YThickness variation Soluble in IPA? N N N N N N N Y

The significance of the acrylic acid component to the dissolution rateof the resulting polymer resin compositions was further evaluated usingvarious ones of the node separation polymers prepared as noted inExamples 1-7. Substrates were coated and then “developed” using the samedeveloping composition in order to compare the relative performance ofthe competing polymers with respect to node separation polymers.

The test substrates were coated with the various experimental andcomparative compositions noted above. In light of the data providedabove, the rate of dissolution was taken into account when setting thedevelopment period to ensure that a polymeric buffer layer having athickness of about 20,000 Å and then hardened. The polymer resincompositions according to experimental Examples 1-7 and the comparativeexample were then evaluated. None of the conventional etch and cleaningsteps appear to have much of an impact on the hardened polymer resincomposition, e.g., very little, if any, of the hardened composition wasremoved during exposure to an LAL solution comprising D.I. water,hydrogen fluoride and ammonium fluoride and/or drying steps utilizingIPA.

As reflected above in TABLE 3, the quality of the polymer resin bufferlayers prepared from compositions corresponding to experimental examples1-7 do not exhibit any significant variations of layer quality. Inparticular, the buffer layers prepared from compositions correspondingto experimental examples 1-7 exhibit good film qualities, i.e., does notreflect any significant variations in layer thickness post-development.

While the invention has been particularly shown and described withreference to certain example embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the invention as defined by the following claims.

1. A method of forming a capacitor comprising: forming an insulatinglayer on a semiconductor substrate; forming an opening in the insulatinglayer; forming a conductive layer on an upper surface of the insulatinglayer and a lower surface and sidewalls of the opening; forming a bufferlayer on the conductive layer, the buffer layer filling the opening andincluding a major portion of a copolymer having from 61 to 75 weightpercent benzyl methacrylate; from 8 to 15 weight percent alkyl acrylicacid; and with a remainder being hydroxy alkyl methacrylate; removing anupper portion of the buffer layer using a developer solution to exposean upper portion of the conductive layer, a lower portion of the bufferlayer substantially filling the opening; removing the upper portion ofthe conductive layer to separate lower electrode structures; removingthe lower portion of the buffer layer; forming a dielectric layer on thelower electrode structures; and forming an upper electrode on thedielectric layer.
 2. The method of forming a capacitor according toclaim 1, wherein: the remainder is from 17 to 24 weight percent.
 3. Themethod of forming a capacitor according to claim 1, wherein: thecopolymer has a mean molecular weight of 6700 to
 7500. 4. The method offorming a capacitor according to claim 1, wherein: the copolymerincludes at least three monomers and has a structure corresponding toFormula I:

wherein the variables L, M and N represent the relative molar fractionsof the monomers and satisfy the expressions0<L≦0.8;0<M≦0.25;0<N≦0.35; andL+M+N=1; and, wherein R¹, R² and R³ are independently selected fromC₁-C₆ alkyls and derivatives thereof.
 5. The method of forming acapacitor according to claim 4, wherein: the variables L and M alsosatisfy the expressions45≦L≦0.65; and0.15≦M≦0.25.
 6. The method of forming a capacitor according to claim 5,wherein: N also satisfies the expression0.20≦N≦0.27.
 7. The method of forming a capacitor according to claim 5,wherein: the alkyl acrylic acid consists essentially of methyl acrylicacid and M also satisfies the expression0.17≦M≦0.25.
 8. The method of forming a capacitor according to claim 4,wherein: the alkyl acrylic acid is selected from a group of consistingof the C₁-C₄ acrylic acids and mixtures thereof; and the hydroxy alkylmethacrylate is selected from a group of consisting of the C₁-C₄ hydroxyalkyl methacrylates and mixtures thereof.
 9. The method of forming acapacitor according to claim 8, wherein: the alkyl acrylic acid includesa major portion of methyl acrylic acid; and the hydroxy alkylmethacrylate includes a major portion of hydroxy ethyl methacrylate. 10.The method of forming a capacitor according to claim 4, wherein: thealkyl acrylic acid consists essentially of methyl acrylic acid; and thehydroxy alkyl methacrylate consists essentially of hydroxy ethylmethacrylate.
 11. A method of forming a semiconductor device comprising:forming an electric element on a semiconductor substrate; forming aninsulating layer on the electric element; forming an opening in theinsulating layer to expose a contact region on the electric element;forming a conductive layer on an upper surface of the insulating layerand a lower surface and sidewalls of the opening; forming a buffer layeron the conductive layer, the buffer layer filling the opening andincluding a major portion of a copolymer having from 61 to 75 weightpercent benzyl methacrylate; from 8 to 15 weight percent alkyl acrylicacid; and with a remainder being hydroxy alkyl methacrylate; removing anupper portion of the buffer layer using a developer solution to exposean upper portion of the conductive layer, a lower portion of the bufferlayer substantially filling the opening; removing the upper portion ofthe conductive layer to separate lower electrode structures; removingthe lower portion of the buffer layer and the insulating layer; forminga dielectric layer on the lower electrode structures; and forming anupper electrode on the dielectric layer.
 12. The method of forming asemiconductor device according to claim 11, wherein: the developersolution includes from 1 to 5 wt % tetramethyl ammonium hydroxide in anaqueous solution.
 13. The method of forming a semiconductor deviceaccording to claim 12, wherein: removing the upper portion of the bufferlayer using a developer solution maintains an average removal rate of atleast 30 Å/second.
 14. The method of forming a semiconductor deviceaccording to claim 11, wherein: removing the lower portion of the bufferlayer includes an ashing process that maintains an average removal rateof at least 150 Å/second.